A New pH Sensor Using the Fluorescence Quenching of Carbon Nanotubes

A new pH sensor based on carbon nanotubes (CNTs), which consist of a fluorescent molecule and a CNT attached to each chain end of a pH sensitive polysulfonamide, respectively, is synthesized, and its pH sensitivity is examined in terms of the fluorescent quenching efficiency of the CNT. The pH sensitive polymeric linker shows an abrupt conformational change between an expanded coil structure and a collapsed globule structure, which results in the drastic on-and-off fluorescent quenching efficiency because of the change in the distance between the fluorophore and CNT. This CNT-based sensor responds to a small change in pH with well-defined on-and-off behavior, and also shows an excellent reversibility against pH change, which explains its feasibility to be widely used in the areas of biological and environmental applications.